Cruise Control for the Ducato

On long trips my legs are increasingly tired. Time for a cruise control to be fitted to
the Fiat Ducato.

Our Ducato service agent recommended we fit a unit that they also fit to the X250 model Ducato as
an after-market addon. It is a Drive-by-Wire unit and so is much less intrusive than the older vacuum
units commonly fitted to the 244 Ducatos.

The control unit is a Lite-On Automotive Command Auto Group
AP900 Cruise Control. The AP900 series is a professional Drive-By-Wire Cruise Control and Speed
Limiter system especially designed to fit drive-by-wire vehicles where there is an electric pedal.
In order to get the correct settings, the AP900 Cruise Control programs all parameters by itself
using a new "self-learning" technology.

The command module is a Command CM30 Stalk Switch. It is mounted on the left side of the steering
wheel column.

We were charged $863.64 for the installation, which was done on 9 September 2011 by
TheOneStopShopAustralia. This at first seems high, but a
year ago we had a vacuum cruise control fitted to a Rav4 for over $750. So there is value here.

However, a drive to and from Ballarat showed the cruise control to be poorly set up. It would
cause the Ducato to slow down at the bottom of hills and to speed up at the crest. It was also very
unresponsive to commands to increase or decrease the speed. A phone call resulted in a chap from
TOSSA coming to our home and taking the Ducato out to teach the unit to behave.

Subsequently, driving to Sydney around the coast showed me that while the responsiveness to
commands was improved, the response to changes in speed was not — the van was dangerous
in traffic, exceeding a set speed of 90 kph by 10 kph or more at the top of a crest!

I emailed Command Auto Group and got a response! Their technical support officer discussed the
issue and diagnosed that the feedback loop GAIN of the controller was not high enough. He sent
the programming instructions by email, and as I headed north from Sydney I experimented with the
setting options. I found that the Pedal Calibration was not correct and had to be repeated, the
INIT command had been set to 8 (range 1...15) and the GAIN had been set to 5 (range 3...14).
After much frustration I settled on an INIT setting of 10 and a GAIN of 14.

With over 8,000 km of experience with the AP900 I have to say I am disappointed. The controller
works well in flat terrain, but in undulating conditions it continues to slow down at the bottom of
dips and speed up at the crest. Now, however, the overshoots are usually reduced to about 5 kph or less
at a set speed of 90 kph. This is still by far the worst performance I have ever experienced from
a cruise control.

It appears that the AP900 does not respond quickly enough to a speed change, even when the GAIN
is set to its maximum of 14. And that is all it responds to, not rate of change of speed, not
anything else. Its a very simple proportional controller and it does not even do that very well.
I've spent a lot of money for a not-so-good product.

Update

A year later, September 2012, I contacted Command Auto Group again, wondering if there has been an
update to the firmware of the AP900 to increase the slew rate of the controller. They offered to test
my unit if I would send it to them. To do so, I devised a plug to take the place of the controller
so the vehicle was still usable while the controller was absent:

The accelerator in the Ducato 2.8 JTD consists of two rheostats, a main and a safety integral
potentiometer. The AP900 takes over from these potentiometers by inserting itself in the wiring as
shown. A replacement plug for when the AP900 is absent simply bridges the cuts in the wires to Point
4 and Point 6 on the accelerator.

Command Auto Group could not find anything amiss with my AP900 controller. They returned it along
with a new controller programmed for the settings that they believe I should be using. Great service,
however there has been only a slight improvement in the behaviour of the AP900. I need to experiment
further.

User Commands for the Cruise Control

There is also a SPEED LIMITER function:

Pressing the ON/OFF key for more than 1 second will turn the Speed Limiter ON or OFF.
The various functions are analogous to the Cruise Control functions.